MATLAB Answers


Apply a mask to 4D medical images in a vectorized way

Asked by AP
on 11 Feb 2013

Dear All,

I have a 4D array V, with the size [144 144 12 25]. In fact, it is a 4D medical image with 12 stacked slices in 25 different time. I want to apply a mask, named M, to each image in the array in a vectorized way. M is a 144x144 array containing logical values. Could someone help me how to do it?



  1 Comment

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2 Answers

Answer by José-Luis
on 11 Feb 2013
Edited by José-Luis
on 12 Feb 2013
 Accepted answer

 data = rand(144,144,12,25);
 your_mask = rand(144,144) > 0.5;

Assuming you want to multiply by the mask:

 your_result = bsxfun(@times,data,mask);

Note that you can do operations other than multiplication. Please have a look at

 doc bsxfun


Isn't that what you want?


I want the operation on each image. I thought bsxfun is only for each pixel and can't be applied to each image in a 4D array. Please correct me if I am wrong: so when we call bsxfun(@times,data,mask), bsxfun applies the mask to each 144x144. Is that right?

Yes. That's what the "singleton expansion" in the documentation means.

Answer by Conrad
on 11 Feb 2013

Something like this:

fV = V.*M(:,:,ones(1,size(V,3)),ones(1,size(V,4)));



How can I convert M, with size [144 144] to M with [144 144 12 25]?

I think, I have to use

repmat(M, [1 1 size(V,3) size(V,4)])

to duplicate M in other dimensions and make it [144 144 12 25].

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